Traffic monitoring and control system



p 27, 1966 J. L. BARKER 3,275,984

TRAFFIC MONITORING AND CONTROL SYSTEM Original Filed Feb. 5, 1959 5 Sheets-Sheet l DELAY AHEAD TAKETHIS EXIT DO NOT ENTER EXPRESSWAY CDNGESTED MONITORNQ AND ROL CENTER 23 HOLD ALARM NORMA REMOTE UMP MQT mama S LJ OFF RE E E ALARM! o o I 4007 00' 400". now.

VOLUME RAYE OF QNAN'IE RES .25 4

0 TIME HOLD/RELEASE DELAY $7220 RATE OF CHANGE SELECTOR I VOLUME COMPUTER CHANGE IN /o/MINUTE FOR FULL SCALE ON METER M SPEED cor WT] CHANGE 1N MPH/MINUTE FOR FULL SCALE ON METER FIG. 5

INVENTOR. JOHN L BARKER ATTORNE Y Sept. 27, 1966 J. L. BARKER TRAFFIC MONITORING AND CONTROL SYSTEM Original Filed Feb. 5 1959 SPEED SIGNAL 5 Sheets-Sheet 2 (PULSE) SPEED 34 TO SPEED RATE VEHICLE? SPEED 1 AVERAGE T OF CHANGE I7\ PASSAGE ND 32 COMPUTER 36 COMPUTER AND SPEED k V U VOLUME PASSAGE E EELN 2 IXAFULSE SIGNAL (PULSE) VOLUME 32 RATE T 0 TR NSLATOR z- 33 COMPUTER 37 COMPUTER FIG 2 a.

45 NEGATIVE CHANGE FROM RANGE ADJUST q COINCIDENCE UNIT 52 SPEED 47 Q?) (RELEASES RELAY VSL AVERAGE T wHEN BOTH INPUTS COMPUTER DIFFERENTIATING I EXCEED MINIMUM -r- CIRCUIT I jv NEGATIVE LIMITS) 36 RATE OF CHANGE 4| HI OF SPEED E FROM VOLUME I .2 42A CH COMPUTER DIFFERENTIATING I CIRCUIT 4 at 3? RATE OF CHANGE VI EOQPBEOETDH P OF VOLUME I I.) 39 DECREASING SUBSTANTIALLY I. ll 56 56 RESET LIMIT ADJUST INSTANT TIME I 46 I (DUAL) ALARM 6| DELAY 58 54 62 HOLD/RELEASE 6O r4l SELECTOR 63 64-IM NEAL] 66 POSITIVE CHANGE 4(RELEASE) COINCIDENCE UNIT 65 73 (RELEASES RELAY VSH DELAYED WHEN BOTH INPUTS |ND|CATOR EXCEED MINIMUM POSITIVE LIMITS) $74 I I6. 2 C E 63 I (AT PRECEDING 60 56 25 ExIT RAMP) I L DELAY AHEAD I OUTPUT FOR BOTH LIMIT ADJUST VOLUME a SPEED TAKE THIS EXIT DUAL) INCREASING SELECTOR SUBSZANT'ALI-Y I TIME SWITCH E f 27 7O DELAY R g ggE w E (AT ENTRANCE mgf wg 7 72 CONGESTED RAMP OR RAMPS) INVENTOR. JOHN L. BARKER 27 By E BARRIER F (OR GATE) 32 wake Zf 2M ATTORNEY Sept. 27, BARKER TRAFFIC MONITORING AND CONTROL SYSTEM 5, 1959 5 Sheets-Sheet 3 Original Filed Feb.

Fm mo v9 Gww 502mg INVENTOR.

JOHN L. BARKER ATTORNEY United States Patent TRAFFIC MONITORING AND CONTROL SYSTEM John L. Barker, Norwalk, Conn., assignor to Laboratory for Electronics, Inc., Waltham, Mass., a corporation of Delaware Continuation of application Ser. No. 791,460, Feb. 5, 1959, now Patent No. 3,237,154, dated Feb. 22, 1966. This application May 27, 1965, Ser. No. 459,284

12 Claims. (Cl. 340-31) This invention relates to a system for monitoring traffic and responding to particular changes in conditions of traffic flow such as volume and speed, to indicate such changes, and to operate alarm devices and remote changeable signs, signals or other devices to guide or control traffic in relation to entrance to and exit from highways or expressways, or to one or more of these features.

This application is a continuation of my copending patent application, Serial No. 791,460, filed-February 5, 1959, now US. Patent 3,237,154, issued February 22, 1966. The present application is directed more particularly to certain aspects of the subject matter disclosed in said parent application but not claimed in said Patent 3,237,154, as more fully set forth below.

Certain aspects of the disclosure of the present application, particularly relating to response to concurrent rates of change in traflic volume and traffic speed of predetermined amounts and directions of change, for example, are repeated to some extent from said parent application for convenience of reference and understanding in the present application, but are claimed in said Patent 3,237,154. Reference may be had to the aforesaid patent for further features and details of response to concurrent changes in speed and volume.

The present application is more particularly directed to aspects of the invention relating to sensing or determining and responding to the rate of change of a traiiic flow characteristic such as traflic volume or trafii-c speed alone.

In a preferred form of one aspect of the invention, the present application provides means for sensing vehicles in a stream of trafiic and producing an electrical signal, such as a voltage, representing a varying characteristic of traffic flow as averaged over a period of time or number of vehicles, producing therefrom a further electrical signal or voltage as an output representative of the rate of change of the first electrical signal, and representative of the rate of change of said tratfic flow characteristic. Such output or a predetermined such output may be used for operating an indicator, alarm or tnaffic control device. In one preferred form such further electrical signal (for rate of change) is compared with a reference to provide an output in response to such further electrical signal having a predetermined amount or value representing a rate of change of predetermined amount and direction, which output may be used to operate the indicator, alarm, or trafiic control device.

From further aspects, the invention relates to electrical apparatus for determining the rate of change of traffic volume and the rate of change of tnafiic speed and indicating or responding to selected such changes of predetermined degree, which may be adjustable. Thus the apparatus may be arranged to respond to decreasing traffic volume alone, or to decreasing speed alone, or to increasing speed or volume, or to a combination of increasing speed and increasing volume, or to a combination of increasing. speed and decreasing volume, or to a combination of decreasing speed and increasing volume, or to concurrent decrease in both speed and volume, where response to or indication of such individual conditions or combination of conditions is desired.

In its preferred form, the present apparatus senses the 3,275,984 Patented Sept. 27, 1966 "Ice trafiic changes by deriving the rate of change of the average speed and/ or the rate of change of the traffic volume.

Some aspects of the invention may be applicable to field-s other than traflic, as in the determination of rate of change of a varying average over an adjustable range or beyond a selectable limit or critical value.

The great increase in the volume of vehicular traffic on streets and highways in recent years has resulted in many of such roads becoming overloaded or congested at times despite the continued building of new road facilities. In this connection, the term trafiic volume is used in its generally accepted sense of the rate of trafiic flow past a given point in number of vehicles per unit of time, such as vehicles per hour for example.

Modern high type traffic road facilities such as expressways, freeways, parkways and the like, generally limit access to widely spaced entrance ramps and exit ramps, avoid cross trailic by over-passes or under-passes, and provide multiple traffic lanes and easy curves and are designed for heavy traffic at relatively high speeds. Such high type highway facilities are very costly to build and are involved in the transport of essential goods and the transport ofpeo'ple' to and from work, in many cases, as well as for pleasure.

Even in the best of such high type facilities, most or all of the roadway may be blockedin one direction by a major accident, and in periods of heavy trafiic volume, a relatively small accident or minor breakdown in one lane or some local change in road or visibility conditions may so impede trafiic that the flow of traffic is suddenly slowed down to a very low level and the effective capacity of the roadway is so reduced that long lines of traffic may accumulate with large numbers of vehicles stopped or waves of stopping and starting and moving at very low speeds may move back along the line of trafiic.

The accumulation of such stopped or very slow'moving traflic, may extend back several miles from the obstruction before traffic authorities are aware of the situation, and in many cases, because of hills or curves in the road, other drivers approaching the trailing end of the line of slow moving traffic will not realize the situation until they have passed a possible exit or other alternate route.

Certain sections of the roadway may be more susceptible to such conditions than others, but in any event, it has been a serious problem to notify traffic authorities or the traffic itself, or both, of such congested trafi'lc conditions as soon as possible, both from the viewpoint of getting aid to accident victims promptly and from the viewpoint of expediting traffic and diverting it if necessary as soon as possible.

The sensing of sustained low speed alone below a pre selected critical speed as by a succession of such speeds of vehicles, may give indication of trafiic obstruction or the like in some instances. Apparatus for responding to a succession of below critical low speeds of vehicles in traffic, and operating an indicating device or alarm device therefrom, is disclosed and claimed in a copending patent application Serial Number 777,711, entitled, Traffic Speed Monitor, filed December 2, 1958, now US. Patent 3,024,- 443, issued March 6, 1962, in which I am a joint inventor with Bernard J. Midlock. Such apparatus may be used as a means for determining sustained low speeds in certain traffic control systems as some aspects of the present invention as appears below.

However, speed alone may also decreasewith increasing traflic volume before the latter reaches a critical level approximating the practical capacity of the road. It is known to t-rafiic authorities that if more traffic then arrives on the road tending to exceed this critical level, the actual trafiic volume and speed will both drop sharply, and the effective capacity will be much reduced. Environmental factors also such as weather and road condi- 3 tions such as ice, snow, wet pavement or fog will often cause marked shifts in a critical level of volume or of speed.

Thus, the impedance or congestion of trafiic popularly known as a traffic jam, may arise because of an accident, road conditions, or other factors at moderate or relatively low traflic volume as well as arising at times of high traflic volume, and the problem has been to identify automatically by some means the congestion or substantial impedance of trafiic over a wide range of traflic volumes and speeds.

Most people are familiar with the fluctuations normally encountered in normal trafiic flow over any given time period, and thus decreasing tratfic volume alone would not necessarily indicate traflic congestion.

It is an object of the invention to determine and indi- 1 cate the rate of change of traffic volume with respect to time and the rate of change of trafiic speed with respect to time in relation to running averages of such volume and speed.

It is another object of the invention to sense a predetermined minimum or threshold value of rate of change of traflic volume or trafiic speed in a predetermined direction of change for indicating, alarm or control purposes.

It is a further object of the invention to provide a method or means of trafiic control by sensing restriction of trafiic flow by sensing substantial reduction in trafiic speed and/ or trafiic volume at a point on a roadway and to operate or control a trafiic sign and/or signal to warn of and/or to relieve such restriction.

It is also an object of the invention to provide a method or means for monitoring traific along a highway or expressway by sampling traffic speed and traflic volume at one or more points thereon, computing running averages of traflic speed and trafiic volume, and determining there from at a remote or central monitoring point the rate of change of speed and the rate of change of volume over a scale from negative to positive values, and providing indications or alarms or both at such remote point.

Other objects of the invention may be apparent in the following description and appended claims with reference to the accompanying drawings in which:

FIG. 1 shows a plan view of spaced sections of a roadway such as an expressway or freeway, illustrating one application of speed and volume change sensing equipment for remote monitoring and control of traffic signs and related devices.

FIG. 2, comprising the SUB-FIGURES 2a, 2b, and 20, illustrates in block diagram form a preferred form of trafiic monitoring and control system for sensing particular changes in traflic speed and volume and responding to such changes.

FIG. 3 shows in schematic form a preferred circuit diagram of a Volume and Speed Rate of Change Unit apgearing in part FIG. 2b of FIG. 2 and of certain associated ilarm and control products of part FIG. of FIG. 2.

FIG. 4 illustrates the indicating, adjustment and control )E1Hl of a preferred form of Volume and Speed Rate of Ihange Uni-t for responding to concurrently decreasing 'olume and speed, of the type shown in FIG. 2b and IG. 3.

'FIG. 5 shows another form of exit ramp arrangement mploying detection of traific congestion on the ramp to perate a warning sign on the expressway approaching he ramp, or other tIafii-c control device.

Referring now to FIG. 1, there is shown a part of an xpressway or freeway of the usual divided roadway type, f which only about one half is shown for convenience of lustration. The outer and inner edges 11 and 12 of the )adway for the one direction of trafiic indicated by the rrow 13 extend through the three sections of roadway idicated as spaced some distance apart along the roadway y the breaks 14 and 15, introduced merely for conveniice in the drawing. The central divider strip is indicated v the edges 12 and 16, the latter edge also representing the inner edge of the companion roadway (not shown) for the opposite direction of trafiic.

A detector 17 for sensing vehicle passage and speed is illustrated at the right side of the FIG. 1 at a desired point for sampling vehicular trafiic passing along the roadway in one of trafiic lanes on the roadway. The detector 17 is illustrated over the outer lane, for example, and may be of the type known as Model RS1 Radar Speed and Impulse Unit, manufactured by Automatic Signal Division of Eastern Industries, Incorporated, the assignee of the present application for patent, and more fully described and illustrated in my copending application Serial Number 732,248, filed May 1, 1958, for Traffic Monitoring System, now US. Patent 3,059,232 issued October 16, 1962.

This speed and passage detector 17 develops an electrical signal representing passage of a vehicle and its speed in the associated trafiic lane, this signal being transmitted by a two-wire line 22, such as a telephone line, for example, to the remote monitoring and control center 23, where this signal is translated into separate channels for computing traffic volume and trafiic speed on a running average basis, and particular rates of change of speed and volume are sensed for indicating and alarm purposes and to control automatic or changeable signs or other control devices, as more fully explained later herein. The blocks within block 23 are numbered to correspond to their respective counterparts in FIGS. 2a and 2b, for example.

The monitoring and control center 23 may control via line 24 an electrically operated changeable sign 25, for example, in advance of exit ramp 26 to direct trafiic to this exit in case of sensing traffic congestion or impending congestion at the sampling point by a combination of decreasing average speed and decreasing volume. Similarly, the center 23 may operate another changeable sign 27 via line 28 to direct traffic from entering the expressway on entrance ramp 29. A traflic barrier or gate 32 0f the remotely controlled or automatic type may be 0perated as a supplement to sign 27, if desired.

Other speed and passage sensing directors may be located over other lanes as indicated by such detectors 18 and 19. These may be in addition to detector 17 or one or the other may be connected to the remote center 23 instead of detector 17. If only one detector such as 17 is used, it will be in whichever lane is most representative of changes in traflic volume and speed on the roadway, particularly in case of congested traflic conditions.

For continuous monitoring on all lanes, the several detectors 17, 18 and 19 would be individually connected to the monitoring center 23 by additional channels or lines not shown, and the center 23 would have individual translating, computing and rate of change response units preferably, although their outputs might be combined for alarm control circuitry.

FIGS. 2a, 2b and 2c are arranged to be connected to- I gether, as indicated by the corresponding numbered lines and together represent a complete trafiic speed and volume sensing and concurrent rates of change sensing, indicating and control system, although certain features may be omitted in some instances, as desired. For example, the sign or gate control featured on FIG. 20 may be omitted if it is desired to use the monitoring, indicating or alarm features as one aspect of the invention, as in FIGS. 2a plus 2b, or as in FIG. 2b, where average speed and volume inputs are available.

FIG. 2a shows in block diagram form the vehiclepassage and speed sensing detector 17 22 to a speed and impulse translator 31, which is preferably, but not necessarily, located in the remote monitoring and control center 23 of FIG. 1. This translator and its connection separates the combined speed and passage signal into its speed pulse or signal on line 32 and passage pulse or signal on line 33. This translator 31 is more fully disclosed in my copending application Serial Number 732,- 248, above referred to, and its details are not material to the present invention.

The speed signal pulses from individual passing vehicles are in the form of a direct current voltage substantially proportional to speed and are fed into the speed average computer 34 which is also disclosed in my said eopending application, Serial Number 732,248, and provides an electrical voltage output on line 36 representing a running average of the latest, adjustably predetermined number of vehicles.

The volume or passage pulses for the individual vehicles are of the voltage change type, as provided by operation of a relay contact, for example, and are fed to the volume computer 35, which is also disclosed in my said copending application, Serial Number 732,248. This volume computer provides an output voltage on line 37, representative of a running average of .the average number of vehicles passing the sampling point per unit of time over the latest adjustably predetermined time period, which may be of the order of several minutes, for example.

Thus the details of the components and connections of FIG. 2a are all the subject of prior patent applications, and are illustrated here as examples of means for sensing vehicle passing and speed and providing an average speed output signal voltage and a traffic volume output voltage which also serves as an averaged value as contrasted with an instantaneous value.

The respective output voltages representingaverage speed on line 36 and average volume on line 37 serve as inputs to diiferentiating circuits 38 and 39 respectively, in FIG. 2b, to determine the rate of change of speed as a voltage output abbreviated ds/dt on line 41 and the rate of change of volume as a voltage output abbreviated dv/dt on line 42. These rates of change are indicated on the respective meters 43 and 44, each of which is calibrated in percent between negative and positive scale limits with a center zero. Different ratios of the rate of change to the scale and to the output voltage on line 41 or on line 42 respectively may be obtained by the range adjustments indicated at 45 and 46 for the respective rate circuits. Similarly, the blocks 47 and 48 indicate resets for the respective rate circuits. These may be manually operated or by remote controlled relays, for example, to reset the rate circuits to zero, if desired.

The rate output lines 41 and 42 extend as lines 41' and 42 respectively and feed int-o the negative change coincidence unit 52 and may also extend into a positive change coincidence unit 53, on lines 41 and 42 as branches of lines 41' and 42' respectively.

These change response units operate as more fully disclosed in connection with the circuit diagram of FIG. 3, but serve to respond to concurrent rates of change beyond predetermined minimum limits in the stated direction, with such predetermined limits for speed and volume rates individually adjustable as indicated by the block 54 for the negative change response unit 52 and by the block 55 for. the positive change response unit 53. Considering further, the negative change coincidence unit 52, it will be noted that it is indicated that this responds to concurrent negative values of rates of change of both'speed and volume by releasing relay VSL to close its associated contacts to provide an output on line 56. These relay contacts are of the normally closed type, i.e., they are closed only when the relay is deenergized, but these contacts are normally held open by energization of the relay through the action of the associated circuit shown in FIG. 3, in absence of concurrent negative rates, characterizing decreasing speed andvolume, beyond the limits set by the dual individual adjustments 54.

The output line 56 is connected by a branch to an instantaneous indicator or alarm 57, and by another branch to a time delay device 58, which after a predetermined time of persistence of its input provides an output to line 6% and also via line 61 to the Hold/Release Selector 62. The output on line may be used for generation of other devices, such as remotely located indicators, alarms, or trafiic warning or control signs or devices.

The hold-release selector 62, as shown more fully in 6 FIG. 3, controls the action of the delayed alarm or indicator 63 and the associated output line 66 by determining whether the delayed alarm 63 and the output on line 66' will be maintained only as long as the concurrent negative change indicating output on line 56 continues or will be held or maintained after such indicating output on line 56 ends, as when the traflic volume and speed are no longer decreasing sufiiciently.

In the hold condition, the output on line 66 and 66 and the operation of the alarm or indicator 63 is sustained until release by manual switching of this selector 62 to a release or non-hold position, or by manual operation of a remote release switch 64, or by automatic remote release via line 65, for example. Any other or remote devices which may be connected to line 66' will also be held in activated condition by the hold-release selector 62 when the latter is set to the hold condition and until released in a manner similar to that described above in relation to delayed alarm or indicator 63.

The other or remote devices may alternatively be connected to line 60, so that they will release automatically upon ending of output on line 56, and consequent reset of the time delay unit 58. The latter provides its time delay between the start of active output on line 56 and the start of output on lines 60 and 61, and after such output on line 56 has persisted for such time period, but this unit 58 is immediately resettable to terminate its output on 60, 61 if there is any interruption of output on line 56, which serves as the input to this time delay unit 58. This unit 58 acts as a slow-operate, quick release time delay relay.

The part of FIG. 2b described above corresponds in general to the circuit diagram of FIG. 3 presenting a speed and volume rate of change unit which responds to concurrent nega-tive rates of change exceeding the limits set. There is also shown in FIG. 2b a speed and volume rate of change unit for responding to concurrent positive rates of change exceeding set limits as briefly mentioned above.

The latter unit is shown in the lower right part of FIG. 2b. Thus branches 41" and 42 of the rate of change output lines for speed and volume respectively extend downward to feed these outputs into a positive change coincidence unit 53. This unit 53 is the same as the corresponding negative change coincidence unit 52 above except that the diodes shown in FIG. 3 associated with the input circuits 41" and 42 would be reversed in unit 53 to respond to positive coincidence or concurrence of inputs instead of negative concurrence of inputs, and in connection with unit 53 the limits adjustment 55 for response would be set as desired for the minimum positive rates of change to which it is desired to respond.

The concurrence of positive rates of change of both volume and speed beyond the set limits releases the relay VSH in unit 53 in the same manner as concurrence of negative rates of change releases the corresponding relay VSL in unit 52. The release of relay VSH closes its contact shown in FIG. 2b to provide an output on line 7% in response to concurrence of positive rates of changes beyond the limits set by adjustor 55 and thus representing concurrent substantial increase in both trafiic volume and speed.

This output on line 76 operates an instantaneous indicator 71 and a time delay untit 72 which, after a sufliciently long continued such output on line 70, will operate the delayed indicator 73 via line 74. A further output line 65 is shown from the time delay unit 72 and serves as an automatic remote reset or release of any previously set up delayed alarm 63 or associated devices which may be held operated after initial actuation by the time delay unit 58 and the hold-release selector 62 when the latter is set to its Hold-Remote Reset position as indicated on the control panel of the assembly shown in one preferred form in FIG. 4, for example but without limitation thereto.

The two outputs 74 and 65 from delay unit 72 are shown to illustrate both make contact and break contact operations, since the delayed indicator 73 and other such devices would ordinarily operate from make contacts and since the reset or release through the hold-release selector is illustrated in the circuit diagram as of the series type employing the opening at least momentarily of a normally closed contact, such as shown in the box marked remote reset in the lower right corner of FIG. 3. This contact may be of the manually operated pushbutton or momentary opened contact type or may be a break contact on the output relay of the time delay unit, represented by the designation 64 or 65. A corresponding such break contact 65' is illustrated on the output relay TL in the time delay unit 58 of FIG. 3 for example, and it will be understood that a corresponding break contact on the output relay (not shown) may be provided in time delay relay 72. It will be appreciated that electrical devices may readily be arranged to operate from either make contacts or from break contacts as desired, and the circuit arrangements are for purposes of illustration.

It will also be understood that other indicator, alarm or control devices may be connected to line 74 to be operated thereby, and that if desired to use the positive change unit 53 as an independent indication of positive change coincidence instead of for reset of the negative change coincidence alarm, the positive change may have a hold-release selector for control of indicator 73 or the like for example.

FIG. illustrates in more detail several types of traflic control or warning devices which may be operated by one of the outputs 56', 60 or 66 derived from the output 56 of the negative change coincidence unit 52. Thus in FIG. 20 all three lines 56', 60 and 66 are shown with a switch for selecting among them for the type of control desired. The line 56 would provide instantaneous control, the line 60 would provide delayed control and the line 66' would provide delayed control subject to the action of the hold-release selector 62. The switch in FIG. 2c is shown in position connecting the latter line 66 to operate the electrical illuminated or changeable signs and 27, as Well as the barrier or gate 32, these reference numbers corresponding to the same devices in FIG. 1.

It will be noted in FIG. 2c that sign 27 is indicated as part of a larger sign and signal assembly, including a red or stop signal R which is operated with the sign, and a cautionary or flashing signal F operated when the sign is not operated, the operation or non-operation being under the control of the relay indicated. It will be appreciated that these signs and other devices are illustrative and other forms may be used or the signals or some of the other features might be omitted in some instances.

The circuit diagram comprising FIG. 3 illustrates a preferred form of electrical apparatus corresponding to the I-block diagram of FIG. 2b, but illustrating particularly the upper part of FIG. 2b involving response to concurrently decreasing speed and volume and the associated alarm circuitry, without the positive change response unit 53 and its associated indicators 71 and 73 and time delay unit 72.

The positive change response unit 53 and such associated elements of FIG. 2b relate to the response to concurrently increasing speed and volume, and may be used alone in some instances as a suppliement to the concurrent decrease response p art above if desired in accordance with the types of response desired for the intended use.

As mentioned above, however, if the rectifier pairs associated with input lines 41 and 42' at the left in the broken line 52 of FIG. 3 are all reversed from the manner shown, and the relay designation VSL changed VSH, then the part of FIG. 3 designated 52 will serve to illustrate the positive change response unit 53, it being assumed in such case that the limit or threshold adjustments '54 or 54(s) and 54(v) also will be set to the desired higher positive voltage value equivalent to a meter reading substantially above zero on its scale, which zero in turn may be equivalent to some convenient intermediate voltage value on a scale of positive voltage values of the same polarity, as positive for example in the preferred form illustrated.

Operation of the speed rate of change measuring circuit, including diiferentiating circuit 38, range adjust 45 and reset 47 will now be described more fully with reference to FIG. 3. It should be noted that the volume rate of change measuring circuit is an exact duplicate of the speed rate of change measuring circuit, therefore the circuitry details of the volume rate of change measuring circuit are not shown within the block 87, but the detailed circuitry above in the corresponding speed rate of change measuring block 88 serves to illustrate both. The procedure of calibration and setting as will be discussed below, as well as operation of the circuitry, apply to both the speed rate of change measuring circuit and the volume rate of change measuring circuit.

Input speed information, in the form of a direct current voltage, from zero, with respect to ground,'to plus volts above ground for example, is applied via lead 36, from the speed averaging computer, through a potential divider including resistors 101, 102, 103 and 104 to ground. The input applied via lead 36 represents the detected running average vehicle speed of the desired last number of vehicles of from zero to 100 miles Per hour.

Input volume information, in the form of a direct current voltage, from zero, with respect to ground, to plus 100 volts above ground for example, is applied via lead 37 from the volume computer to a similar potential divider, not shown, in the circuitry of the volume rate of change measuring circuit 87.

The input applied via lead 37 represents the running average volume of trafiic with 100 volts representing the upper end of the range of traffic volume anticipated, for example. This may for example, be of the order of 2000 vehicles per hour for a typical traflic lane in a roadway having free running traflic, although some lanes might have a lower volume corresponding to the 100 volts. For convenience 100 volts are considered to equal 100% for the upper end of the desired range of tratfic volume.

A multiposition ganged selector switch 76,-including sections 76a and 76b, in conjunction with the associated resistors comprise the range adjust 45, which serves to adjust the sensitivity of the rate measuring circuit, that is, the speed change per unit of time to produce full scale reading on the rate of change meter 43.

A corresponding selector switch and associated circuitry serve as range adjust 46 for the control of sensitivity of the volume rate measuring circuit 39.

The selector switch 76 of range adjustor 45 is illus-v t-rated in FIGS. 3 and 4 in its second position, which may for example correspond to a rate of change of speed of 10 miles per hour per minute for a 100% indication on the meter 43. The rate of change of speed may be expressed as m.p.h. per minute for example for convenience and as a reminder that this is the rate of change of the average speed and is not employed in the frequently used sense of acceleration.

The scale of values of range adjustor 45 shown in FIG. 4 are given as one example of such values in m.p.h. change per minute, but without limitation thereto.

With range adjustor 45 so set for 10 mph. per minute the speed rate of change meter 43 will indicate minus 100% for a decrease in the running average speed of 10 mph. per minute, and will indicate plus 100% for an increase in the running average speed of 10 mph. per minute, the meter having a central zero indication for no change in speed and being linear for intermediate readings as well.

The signal from selector switch section 76a is chan- 9 neled through resistor 108 to capacitor 109, the combination of which serves as a smoothing filter for the signal and to substantially eliminate any sharp changes in voltage that may occur in the signal due to any A.C. pickup or extraneous noise.

The filtered signal is fed through the differentiating network 38 including capacitor 110 and resistor 111, with the differentiated voltage appearing across resistor 111. Selector switch section 76b is ganged to section 76a as previously described and provides a 100% increase in the sensitivity of the unit in the maximum sensitivity or top position as compared to the second position by connection of resistor 112 in series with resistor 111, and resistor 112 is shunted out in all positions except the top position.

The ditferentiated input voltage, corresponding to the rate of change of the speed is applied to the grid of triode 81. Triode sections 81 and 82 are a balanced type voltmeter through which is obtained stability for accurate reading of low voltages. The meter 43 is connected via resistor 113 between the cathodes of triode sections 81 and 82. It will be noted that terminal 85- is connected to terminal 83 via line 86. This connection includes resistor 113 in the circuit between the two cathodes of the two triodes.

It may be desired to by-pass the resistor 113 via terminal 84 and to connect a recorder or remote meter between terminal 84 and terminal 83. In such case the resistance of such recorder or remote meter should ap proximate the value of resistor 113 which may be of the order of 2000 ohms, for example, to maintain the calibration of the unit.

The difierentiated signal is available in voltage form at the cathode of triode 81 and is fed via line 41 and 41' to crystal rectifier 114 in the negative change coincidence unit 52.

The differentiating circuit 38 may be reset by operation of reset 47, which is illustrated as a push-button controlling contacts 118 and 119. Closure of contact 118 shunts out the input series resistance 108 in the filter network to provide a low impedance path for rapidly charging capacitors 109 and 110 while contact 119 shunts out the resistor 111 to provide another low impedance path. The combined low impedance paths insure that capacitor 110 rapidly assumes the potential of the input voltage from the speed averaging computer as applied via line 36 as tapped by switch 76a, and thereby, upon release of the reset pushbutton 47, the unit will read the differentiated input signal from this point on.

Calibration of meter 43 is made by adjustment of two potential dividers, one potential divider including potentiometer 121 and resistor 120 between the cathode of triode 81 and ground, the second potential divider including resistor 125 and potentiometer 126 between the DC. supply and ground. With tap 1 2 7 adjusted to its ground extremity the minus 100% rate indication is calibrated by adjustment of tap 12-2 on potentiometer 121. The zero or center point may then be set by adjustment of tap 127 on potentiometer 126. The latter adjustment in effect determines the voltage about which the circuit will ditfe-rentiate the input signal. Calibration of the circuit would be made with the reset button 47 held closed. After calibration is completed, the reset button 47 serves to reestablish a proper reading more quickly after any change in adjustment 45 for example or when the unit is first turned on.

The output of the differentiating circuit is biased in a positive direction with respect to ground by the potentiometer 126-127, and is applied to the grid of the cathode follower triode 81, and the output of this tube on line 41 is always positive above ground for all indications of meter 43 from minus 100% reading through zero to plus 100% reading of rate of change.

-The differentiated signal on line 41 is applied via lead 41 to crystal rectifier 114 to control the impedance at junction 133 with respect to ground in cooperation with similar rectifier 114 and the limit adjust 54(s), and thus to provide a threshold control for operation of the amplifier tube 135 in response to a difierentiated signal of sufliciently low positive DC. voltage, corresponding to a sufiiciently large negative rate of change of speed, as set by the threshold or limit adjuster 54(s), as more fully described below in connection with the clamping and unclamping of the input to tube 135 under control of the impedance at junction 133.

FIG. 21) illustrates in block form a limit adjust (dual) 54. This illustrates, functionally, two-limit adjusting units, shown in FIG. 3: 54(s) associated with rate of change of speed and 54(v) associated with rate of change of volume.

The limit adjusting units 54(s) and 54(v) are similar to each other and limit adjust 54(s) is in the form of a potential divider including resistors 128 and 129 in series with potentiometer 130 between a positive D.C. supply and ground, and this limit adjust 54(s) serves to set the desired limit or threshold of negative rate of change of speed required for operation of the negative change coincidence unit.

To set the desired decrease as a limit on the limit adjust 54(s), the potentiometer arm 130' may be adjusted so that the positive voltage between arm 130 and ground is of the same value as the positive voltage between line 41 and ground when the meter 43 reads a value of minus 10%, for example. This setting would provide one of the two inputs required for operation of the negative change coincidence unit when a rate of decrease of 10% or more occurs in the average speed.

The negative change coincidence unit provides an indication when both the average speed decreases at a rate exceeding the preset limit as adjusted by the limit adjust 54(s) and the average volume decreases at a rate exceeding the preset limit as adjusted by the limit adjust 54( v). The individual rates of decrease, represented in a percentage, will appear on the respective meters 43 and 44, as for example minus 10%. The speed and volume rate of change signalsfor operation of the-negative change coincidence gate are applied on leads 41 and 42' to rectifiers 114 and 114 and to rectifiers and 15 respectively. When the positive voltage applied via lead 41. at point 133 is less than thepositive voltage applied via arm of limit adjust 54(s) and the positive voltage applied via lead 42 at point 133' is less than the positive voltage applied via the arm of the potentiometer of limit adjust 54(v), an unclamping of the grid 132 occurs and the negative change coincidence unit produces an output. 0

Operation of .the clamping action atthe input circuit to the negative change coincidenceunit will now be explained more fully withrespect to the rate of change of speed circuit, which operation is similar to that of the rate of change of volume circuit.

Sixty cycle alternating .current (A.C.) ofa very low value, 3 volts for example, is connected via high resistance 134 to the grid 132 of triode 135. With thenegative change coincidence unit held clamped, the A.Cpis prevented from acting on the grid 132 by capacitor 138, in combination with diodes 114 and 114? and/or by capacitor 137, in combination with diodes 115 and 115'. With the voltage at lead 41' of a higher value than the voltage at the arm 130' of potentiometer, 130, current flows through diodes 114 and 114' of sufficient magnitude to hold the voltage at junction 133. This etfectively provides an A.C. ground at junction133 and via capacitor 138 to the grid 132.

It has been found that satisfactory operation is provided with the following typical va-lues of components associated with the circuits producing the clamping, but without limitation to such values; resistance 134, 10 megohms; capacitor 138,-1 microfarad; resistance 128,

1 1 82,000 ohms; resistance 129, 3000 ohms; potentiometer 130, 3000 ohms; resistance 136, 100,000 ohms.

Resistors 128, 129 may be reduced or omitted and the value of 130 increased if desired to extend the range of adjustment. Similarly the fixed resistors in limit adjust 54(v) may also be reduced or omitted if so desired.

Thus the output voltage, via leads 41' and 42' of the rate of change of speed circuit and the rate of change of volume circuit respectively, must fall below the voltage set on the respective limit adjust circuits 54(s) and 54(v) in order that the unclamping effect occur and thus provide a clipped A.C. or a chopped D.C. for amplification by the tubes 135 and 140.

This action results from the change from low impedance to high impedance at both junctions 133 and 133'. The increased impedance in the A.C. circuit reduces the current and consequent voltage drop across resistor 134 and allows the A.C. to act on the grid 132.

The applied 60 cycle A.C. is amplified by two high gain stages of conventional resistance capacity coupled amplifiers. The amplified A.C. is then rectified at the anode circuit of triode 140 by means of diode doubler combination 141 and 142. This combination produces a negative D.C. voltage (with respect to ground), which voltage is applied to the parallel connected grids of dual triode 144, which is connected to react as one tube. The applied negative voltage on the grids of dual triode 144 increases the bias of the triode to cut-off. The triode, which is in the energizing circuit for relay VSL materially reduces the plate current and deenergizes relay VSL.

This combination of a high gain amplifier and the clamping-unclamping action described above on the A.C. signal at its input and a rectified output operating the control circuit for relay VSL, provides the sensitivity required to sense the small D.C. rate signals with a high degree of accuracy at the threshold points, and to respond only beyond the desired threshold or thresholds as set by the limit adjustors.

With both inputs from 41' and 42' sufficient for unclamping, relay VSL is deenergized and closes its contacts 151 and 152 and opens its contact 153-. Closure of contact 151 supplies A.C. power, of the order of 110 volts for example, to the instant alarm 57 and to output lead 56'. Closure of contact 152 supplies D.C. positive power to time delay unit 58, while the opening of contact 153 opens the discharge circuit to ground for the timing capacitor 154 in the time delay unit.

The time delay unit, illustrated in the circuit diagram in FIG. 3, blocked off by a broken line box 58 includes a timer which may, by way of example, be of the type illustrated, or may be any conventional timer or delay action relay. The timer illustrated in FIG. 3, in time delay unit 58, is one type of electronic timer that may be employed in the time delay unit. The illus trated timer is of the type disclosed and claimed by Peter C. Brockett in his copending application Serial Number 677,993 filed August 13, 1957, under the name, Electronic Timing Circuit, now US. Patent 2,964,625 and assigned to the assignee of the present invention.

Normally, with relay VSL energized, contact 153 is closed and supplied a ground connection to the upper side of timing capacitor 154 to keep the capacitor substantially at ground potential. This maintains the grid in the left side of triode 170 at ground potential and keeps the left side of the triode 170 biased to cut off while the right side of triode 170 is conducting.

The switch 77 is a multiposition selector switch for selection, as desired, of one or more of the resistors 155 to 161 for inclusion in the charging circuit between the D.C. supply and timing capacitor 154,'to determine the timing interval. j p

-Upon completionof the charging circuit and opening of the ground connection to the upper side of capacitor 154 the charge on the capacitor 154 is increased and the potential applied to the grid in the left side of tube is likewise increased.

- When the potential applied to the grid in the left side of triode 170 increases to an amount as determined by the setting of arm 171 on the potential divider associated with the grid in the right side of the triode 170, the left side of the triode 170 will begin to pass current and the right side of triode 170 will become nonconductive. When the left side of triode 170 becomes conductive a surge of current will pass through the coil of relay TL to energize this relay. 7 I

Energization of relay TL reverses its contacts from the normal position shown, thus providing activation of an alarm 175 and a ground connection to selector switch section 7 8c.

Selector switch section 78c is ganged with switch section 78d in multi-position switch 78, and in its rightmost position as illustrated and in its center position, provides a ground connection for relay RS through contacts of relay TL and line 61 when relay TL is energized. Thus relay RS is energized after the time delay of unit 58, and thus in response to sustained rate of charge beyond the threshold as described above.

Energization of relay RS provides illumination of the delayed alarm 63 as well as an output via lead 66' for control of other devices. Relay RS and selector switch 78 are included in the Hold/Release Selector 62 which is illustrated in block form in FIG. 2b and also shown on the control panel in FIG. 4. Adjustment of switch section 78d to its rightmost position provides a lockin circuit for relay RS via its upper contact which is connected to ground through a remote reset switch 64. Adjustment of switch 78 to its center position opens the lock-in circuit for relay RS but maintains the operating circuit under control of relay TL to be operated and released directly with the latter. Adjustment of switch 78 to its leftmost position disconnects relay RS. Thus switch 78 may be changed from its rightmost position momentarily if desired for local reset,

The relay RS is provided in the preferred circuit illustrated to give greater flexibility of output control and to permit heavier duty contacts to be employed on relay RS While leaving relay TL as a lighter duty relay for example, If desired, however, the functions of these relays might be combined in relay TL by adding contacts and conventional circuitry. 7

Referring again to the time delay unit 58 and its control by the coincidence threshold response unit 52 as shown in FIG. 3, it will be noted that the time delay unit 53 is controlled via two input circuits from contacts of' relay VSL as part of the output of unit 52. These two circuits are 56(a) from make contact 152 and 56(5) from break contact 153.

for charging the time capacitor 154 and opening the discharge or reset circuit therefor could be transferred toa separate relay which might be added in unit 58 and con trolled by a single lead 56 or 56. The circuits 56(11)- and 56(b) in FIG. 3 may be considered a part of control line 56 or 56' in FIG. 2b.

It willalso be appreciated that the time delay unit 58 may be controlled by the circuit 56(1)) from contact 153 alone if the circuit 56(a) were shunted around I the contact 152 to connect directly with the D.C. power aspects of the invention include cooperation of either It will be appreciated that if desired the functions of these contacts in supplying D.C.

of the rate of change circuits with either of the coincidence or threshold response units, as well as cooperation of both rate of change circuits with both coincidence or response units for response to rates of change of traffic volume and traflic speed in opposite directions.

Thus while units 52 and 53 have been referred -to in part above as change coincidence units, particularly in responding to concurrent conditions of changing speed and volume, it will be appreciated that either unit may serve as a threshold response unit either for the rate of change of speed alone by the omission or disconnection of the rate of change of volume unit, blocks 87 and 54(v) in FIG. 3 for example, or for the rate of change of volume unit alone by the omission or disconnection of the rate of change of speed unit blocks 88 and 54(s) in FIG. 3 for example. As an alternative, for selective operation of unit 52 from either the speed unit or the volume unit or both, switches may be placed in the lines above and below junction 131, on either side of capacitors 137 and 138 in FIG. 3, to open or close these circuits individually as desired in unit 52. Similar provision may be made in unit 53 if desired.

Various combinations of units include the speed rate of change unit alone cooperating either with coincidence or response unit 52 alone adjusted for response to decreasing speed alone or with coincidence or response unit 53 alone adjusted for response to increase speed alone, the volume rate of change unit alone cooperating either with coincidence or response unit 52 alone adjusted for response to decreasing volume or with coincidence or response unit 53 alone adjusted for response to increasing volume. Other combinations for response to differrent concurrent conditions include both the rate of change of speed and the rate of change of volume units cooperating with a coincidence unit such as 52 but with diodes 114 and 114 reversed from that shown in FIG. 3 and limit adjust 54(s) adjusted for response to increasing speed and diodes 115 and 115' as shown in FIG. 3 and increasing speed and decreasing volume, or the reverse combination with diodes 114 and 114' as shown in FIG. 3 and limit adjust 54(s) adjusted to respond to decreasing speed and diodes 115 with FIG. .3 and limit adsponse to currently decreasing ume.

speed and increasing volpredetermined directions of same directions or opposite values.

FIG. 4 illustrates a form of control panel that may be employed in one embodiment of the invention.

Similar electrical components that appear in part on the control panel of FIG. 4 and also in FIG. 2b and FIG. 3 are similarly labeled, as for example meters 43 and 44,

range adjusters 45 and 46, limit indicator 57 and remote alarm 63 which may be an alarm itself or an indicator lamp on the panel to show when a remotely located alarm is operated. The time delay adjustment 77 and indicator lamp correspond to similarly labeled components illustrated in FIG. 3. The scale'above the time delay adjuster 77 may be in minutes for example.

Certain blocks on the control panel are expanded below the face of the panel for convenience in the drawing to make the legend appearing thereon legible. Thus the legend, Speed Computer Change in M.P.H./Minute for Full Scale on Meter refers to the scale of figures associated with the adjusting knob of the speed range adjustor 45, and the large horizontal arrow identifies the associated speed rate of change meter 43. Similarly the legend Volume Computer Change in Minute forFull Scale on the Meter associates the range of values of the volume range adjustor 46 above it with the volume rate of change meter to the left. The ranges of values for the several meters and adjustors serve as examples with out limitation thereto.

Neither of the limit adjustors ing the limit adjust 54 appear on the control panel as shown in FIG. 4. It is anticipated that the limit adjustors 54(s) and 54(v) will be varied much less often than the adjustments that appear on the control panel, and thus may be more suitably located'elsewhere in or on the apparatus, but it will be understood that such limit adjustors may be located on the control panel of FIG. 4 if desired.

FIG. 5 illustrates another form of exit ramp from an expressway, parkway or the like, the exit ramp extending from a deceleration lane on the expressway. The arrow 13 indicates the direction of vehicle travel, as the similar arrow in FIG. 1, and the lines 11 and 12 in FIG. 5 represent the limits of one half of the expressway as in FIG. 1 above. The exit ramp 26f terminates at the intersection of a roadway indicated by lines 30 and 30. The bridge 29 indicates that the roadway 30-30 is illustrated as passing under the expressway 11-12 for example.

The diagrammatic showing in FIG. 5 and particularly the length of the roadway 1112 and of the exit ramp 26 in FIG. 5 are condensed or foreshortened for convenience of illustration.

A vehicle speed and passage sensing unit 17, similar to the corresponding labeled detector in FIG. 1, is illustrated over the exit ramp in FIG. 5. The unit 17 would be suspended over the roadway by means of a pole and projecting arm or by means of a span wire, or other means.

54(s) or 54(v) comprisnot to be unduly aifected by ordinary changes in speed The box 23' in block form, represents apparatus mentioned above for responding The line 43 represents an additional output line extendng to a block 40 which block represents a controller which controls the traflic signal 50 through line 51. The :rafiic signal is preferably of the usual type having red, yellow and green signal lights for the several directions, as indicated by the small arrows for example. The controller in block 50 may include one of the well known types of trafiic signal controllers for operating the signal lights through a time cycle to accord right of way to the intersecting roads in sequence, and in addition will preferably include a supplemental preemptive controller for acting through or superseding the normal tralfic signal controller to preempt or otherwise obtain the right of Way for the exit ramp to permit the accumulated trafiic on the exit ramp to be reduced or cleared into the intersection.

Several forms of preemptive control of traffic signals in connection with or superseding a traffic signal controller are illustrated in US. Patent 2,203,871 issued June 11, 1940, to W. R. Koch and in US. Patent 2,234,606 issued March 11,1941, to F. H. Richterkessing.

The preemptive controller may be operated by a thresh old response unit such as 52 from output line 56 for example either in response to substantially decreasing speed alone or in response to concurrently decreasing speed and volume as discussed above, or as otherwise discussed below.

The unit 23 in FIG. may be of the same type as unit 23 above in FIG. 1 for example, or may employ only part of the apparatus shown in the latter. It will be understood that either of these units 23 or 23' may employ both the upper and lower parts of FIG. 2b for concurrent negative change operation response for speed and volume and for concurrent positive change release response for speed and volume, or may employ only the upper part of FIG. 2b for the negative change response without the positive change response, as well as other variations discussed above.

Although preferably the unit 23 particularly would employ response to concurrently decreasing speed and volume of traflic for control of signs or signals, either of the units 23 and 23' and particularly unit 23 in some circumstances might use decreasing speed alone as by only speed circuit 88 and limit adjust 54(s) feeding into threshold response amplifier unit 52, or might use sustained low speed below some value considered critical such as by the successive critical speed response unit of the above mentioned copending application S.N. 777,711 on Trafiic Speed Monitor for example, for control of the signs or signal, or for operation of the preemptive controller for control of the signal to accord right of way to trafiic entering the road 30-30 from the ramp.

The exit ramp may have other well known forms where traffic from the ramp merges with traffic on the other road and is normally free flowing throughout without traffic signal or other stop and go control. It will be understood that the exit ramp may also sweep in an are from the expressway to the right and backward from the far side of the bridge 29 in the familiar clover leaf pattern instead of in the form illustrated in FIG. 5.

It will be understood that the advance warning sign 25' alone may be employed to be opera-ted in response to sustained low or substantially decreasing speed alone or to a combination of decreasing speed and volume, or the preemptive controller may be employed alone to be so operated, or both sign and preemptive controller may be employed as in the preferred form illustrated.

The wording of the signs in the several drawings is primary for illustrative example and other wording may be found suitable in some cases until adoption of some accepted standards for such service.

It will be noted that the term negative rate of change is used to describe a rate of change in the direction of decrease. Similarly a positive rate of change is in the direct on of increase,

Although a number of aspects of the invention and modifications of the form thereof have been described above, it will be understood by those skilled in the art that various other modifications might be made or rearrangements or substitution of parts and the like without departing from the spirit of the invention within the scope of the claims. I claim: 1. A trafiic control system for a roadway including means for sensing a characteristic of traffic flow along said roadway, said sensing means providing an electrical signal output having a running average value representing a running average of said trafiic flow characteristic as averaged over a series of vehicles in said trafiic flow,

means for providing from said output a further electrical signal output having a value representing the rate of change of said average value as representative of the rate of change of said sensed traffic flow characteristic,

indicating means, and

threshold response means coupled to said indicating means and to said further output for controlling said indicating means in response to said further output beyond a predetermined value representing a rate of change in said trafiic flow characteristic beyond a predetermined minimum.

2. A traffic control system as said indicating means includes means for selectively controlling trafiic for permitting said traffic to proceed on said roadway in absence of said output and for diverting traffic from said roadway in response to said output respectively.

- 3. A trafiic control system as in claim 1 and including means for holding said indicating means operated after and despite cessation of said output and until released,

and resetting means for so releasing said holding means.

4. A traific control system as in claim 1 and including timing means for controlling such operation of said indicating means to permit such operation only after a predetermined period of continuous such output.

5. A traffic control system for an exit ramp from an expressway or the like to another road, including means for sensing a characteristic of trafiic flow along said exit ramp, said sensing means providing an electrical signal output having a running average value representinga running average of said traffic flow characteristic as averaged over a series of vehicles in said trafiic flow,

means for providing from said output a further electrical signal output having a value representing the rate of change of said average value as representative of the rate of change of said sensed trafiic flow characteristic,

trafiic control means near one end of said ramp,

and means coupled to said traific control means and to said further output for controlling said traffic control means in response to said further output beyond a predetermined value representing a rate of change in said trafiic flow characteristic beyond a predetermined minimum amount in a predetermined direction of change.

6. A tratfic control system as in claim 5 and in which said traffic flow characteristic sensing means includes means sensing the speeds of vehicles in said traffic flow to provide said electrical signal output as representa tive of the speed of traflic as said traffic flow charaoteristic,

and in which said trafiic control means includes indicating means for traffic on said expressway approaching said ramp,

and said means for controlling said traffic control means includes means for operating said indicating means in response to said further output beyond a predeter mined value in a predetermined direction of change representing decreasing speed.

in claim 1 and in which 7. Electrical apparatus for use with a system having means for measuring a characteristic of flow of vehicular trafiic and providing an electrical signal having a value representative of a running average of said traflic flow characteristic, said apparatus including in combination,

differentiating means adapted to be connected to said traflic measuring means for receiving said electrical value signal, said dilferentiating means producing a direct current voltage output representative of the rate of change of said electrical value, said direct current voltage having a range of values corresponding to a range of rates of change between a maximum rate of decrease through zero to a maximum rate of increase,

a potentiometer connected across a direct current voltage supply and having a movable arm for setting a desired threshold voltage corresponding to a desired rate of change of predetermined amount and direction, and

a circuit including two similarly poled rectifiers and an impedance in series connecting said direct current voltage output and said movable arm;

an amplifier having an input,

an alternating current supply,

a high impedance connecting said alternating current supply with said input, and

a circuit including a capacitor connecting said input to a point between said rectifiers in the first men tioned circuit;

whereby said alternating current voltage will be shunted from said input when said direct current voltage and said threshold voltage have one relation in magnitudes to maintain one of two alternate conditions of conductivity and non-conductivity for said rectifiers,- and whereby said alternating current voltage will be available at said input to be amplified by said amplifier to provide an output in response to a rate of change of at least said predetermined amount and direction when said direct current voltage has a generally opposite relation to said threshold voltage in magnitude to maintain the other of said two alternate conditions for said rectifiers.

8. In combination,

means .for sensing vehicles passing a desired point in a .trafiic lane, said means producing an electrical signal having a running average value representing the running average of trafiic speed of said vehicles in said lane,

diiferentiating means for producing a further electrical signal having avalue representing the rate of change of said average value, and

means for producing an output in response to said further value reaching a predetermined amount in a predetermined direction of change.

9. In combination,

means for sensing vehicles passing a desired point in a traflic lane, said means producing an electrical signal having a running average value reprmenting the running average of trafiic volume in said lane,

differentiating means for producing a further electrical signal having a value representing the rate of change of said average value, and

means for producing an output in response to said further value reaching a predetermined amount in a predetermined direction of change.

10. A trafiic control system including means for sensing traflic flow, said sensing means providing an electrical signal value varying in proportion to an average value of said .traflic flow,

differentiating circuit means connected for receiving said electrical signal for providing an output signal representing the rate of change of said average value of trafiic flow,

biasing means for providing a reference level for said output signal, and

means for providing a control signal in response to said output signal exceeding said reference level of said biasing means.

11. A trafiic control system including means for sensing tratfic flow, said sensing means continuously providing an electrical signal output representing an average value of said trafiic flow over a time period, said electrical signal varying slowly in amplitude with variations in said trafiic flow with respect to time,

a junction,

a condenser connected between said said junction,

a resistor connected between said junction and a reference point, said resistor and condenser being coupled to provide a signal between said junction and said reference point representing the rate of change of said average value,

means for connection to said junction and said reference point for providing a control signal in response to a predetermined rate of change, and means including time delay means for controlling trafiic in response to said control signal when sustained for said time delay. 12. In combination, means for sensing trafiic flow, said sensing means providing an electrical signal varying in amplitude with the average value of said traific flow over a time period, means for diflFerentiating said electrical signal to provide an output signal representing the rate of change of said traflic flow, means connected to said output for indicating the rate of change, threshold bias means, comparison means including a diode, means connecting said bias means for reverse biasing the diode, means connecting said output signal for forward biasing said diode so that rates of change output signal values above said bias result in conduction of said diode, and tralfic control means coupled to said diode to be operated responsive to said diode conduction.

signal output and No references cited.

T. B. HABECKER, Assistant Examiner. NEIL C. READ, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,275,984 September 27, 1966 John L. Barker Column 5, line 22, for "passing" read passage column 6, line 75, after "from" insert time column 7, lin 27, after "change", second occurrence, insert unit line 65, for "instances as a suppliement" read instances or as a supplement line 71, after "line" insert block column 10, line 44, for "15" read 11S column 15,

line 69, for "primary" read primarily Signed and sealed this 26th day of November 1968.

Edward M. Fletcher, Jr. EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

5. A TRAFFIC CONTROL SYSTEM FOR AN EXIT RAMP FROM AN EXPRESSWAY OR THE LIKE TO ANOTHER ROAD, INCLUDING MEANS FOR SENSING A CHARACTERISTIC OF TRAFFIC FLOW ALONG SAID EXIT RAMP, SAID SENSING MEANS PROVIDING AN ELECTRICAL SIGNAL OUTPUT HAVING A RUNNING AVERAGE VALUE REPRESENTING A RUNNING AVERAGE OF SAID TRAFFIC FLOW CHARACTERISTIC AS AVERAGED OVER A SERIES OF VEHICLES IN SAID TRAFFIC FLOW, MEANS FOR PROVIDING FROM SAID OUTPUT A FURTHER ELECTRICAL SIGNAL OUTPUT HAVING A VALVE REPRESENTING THE RATE OF CHANGE OF SAID AVERAGE VALUE AS REPRESENTATIVE OF THE RATE OF CHANGE OF SAID SENSED TRAFFIC FLOW CHARACTERISTIC, TRAFFIC CONTROL MEANS NEAR ONE END OF SAID RAMP, AND MEANS COUPLED TO SAID TRAFFIC CONTROL MEANS AND TO SAID FURTHER OUTPUT FOR CONTROLLING SAID TRAFFIC CONTROL MEANS IN RESPONSE TO SAID FURTHER OUTPUT BEYOND A PREDETERMINED VALUE REPRESENTING A RATE OF CHANGE IN SAID TRAFFIC FLOW CHARACTERISTIC BEYOND A PREDETERMINED MINIMUM AMOUNT IN A PREDETERMINED DIRECTION OF CHANGE. 